Basic JavaScript interview questions in english?

 Here’s a list of basic JavaScript interview questions that can help you prepare:

Basic JavaScript Questions

1. What is JavaScript?

   • JavaScript is a high-level, dynamic, and interpreted programming language that is primarily used for adding interactivity to web pages.

2. What are the data types in JavaScript?

   • JavaScript has several data types:
     • Primitive: undefined, null, boolean, number, string, bigint, and symbol.
     • Non-primitive: object.

3. What is the difference between == and ===?

   • == is the equality operator that compares values after type coercion, while === is the strict equality operator that compares both value and type without coercion.

4. What is a closure?

   • A closure is a function that retains access to its lexical scope, even when the function is executed outside that scope. It allows for private variables and functions.

5. What is the this keyword?

   • this refers to the context in which a function is executed. Its value can vary depending on how a function is called.

6. What are callbacks in JavaScript?

   • A callback is a function that is passed as an argument to another function and is executed after some operation has completed.

7. What is an event in JavaScript?

   • An event is an action or occurrence that happens in the browser, such as a click, form submission, or a key press.

8. What are arrow functions?

   • Arrow functions are a more concise syntax for writing function expressions. They do not have their own this, making them useful in certain contexts.

   javascript
   const add = (a, b) => a + b;
   

9. Explain the concept of promises.

   • A promise is an object that represents the eventual completion or failure of an asynchronous operation. It can be in one of three states: pending, fulfilled, or rejected.

10. What is hoisting?

    • Hoisting is JavaScript's behavior of moving variable and function declarations to the top of their containing scope during the compile phase, allowing them to be used before they are declared.

Advanced JavaScript Questions

1. What are the different types of scopes in JavaScript?

   • JavaScript has three types of scopes: global scope, function scope, and block scope (introduced in ES6 with let and const).

2. Explain the prototype chain.

   • The prototype chain is a mechanism in JavaScript that allows objects to inherit properties and methods from other objects through the prototype property.

3. What is event delegation?

   • Event delegation is a technique where a single event listener is added to a parent element to manage events for multiple child elements, reducing memory usage and improving performance.

4. What are modules in JavaScript?

   • Modules are reusable pieces of code that can be exported from one file and imported into another, allowing for better organization and encapsulation of code. ES6 introduced native support for modules with import and export.

5. What is the difference between null and undefined?

   • undefined means a variable has been declared but has not yet been assigned a value, while null is an assignment value that represents no value or an intentional absence of any object value.

6. Explain the concept of async/await.

   • async/await is syntactic sugar over promises, making asynchronous code look and behave like synchronous code. An async function returns a promise, and await pauses the execution until the promise is resolved.

7. What are JavaScript decorators?

   • Decorators are a special kind of declaration that can be attached to a class or class method. They are used to modify the behavior of the class or its methods and are part of the proposed JavaScript features.

8. What is the purpose of the bind, call, and apply methods?

   • These methods are used to change the context (this) of a function:
     • call: Invokes a function with a specified this value and arguments.
     • apply: Similar to call, but arguments are passed as an array.
     • bind: Returns a new function with a specified this value and initial arguments, but does not execute the function immediately.

9. What are higher-order functions?

   • Higher-order functions are functions that can take other functions as arguments, return functions, or both. They enable functional programming techniques.

10. What is a service worker?

    • A service worker is a script that runs in the background of a web application, allowing for features like caching, push notifications, and offline access.

Conclusion

These questions cover a broad range of topics in JavaScript, from basic to advanced concepts. Preparing for these can help you demonstrate a strong understanding of the language during interviews. Good luck!